Rest in peace, little pigeon!

It was a typical Tuesday afternoon when an ominous loud thud from the windows interrupted our professor’s passionate lecture. A feather was left stuck on the glass panel, with suspicious blood stains dotting the glass. I spun around and saw faces of horror and trauma – they had all, unfortunately, witnessed the full speed collision of an unsuspecting bird into the window.

Victim of the bird-building collision, a male Pink Neck Green Pigeon
Photo by Lim Chun Wei

A few weeks ago, in the same room, we learnt that bird-building collision (also known as window strike) is not a rare occurrence in cities. In the United States alone, an estimated 97.6 to 975.6 million birds die each year from window strikes (Klem, 1990). The worldwide death toll is estimated to be in the billions (Klem, 2008)! Singapore, however, does not have a comprehensive study on this issue. To change things up, the Bird Group embarked on a five-year study of migratory bird collisions in Singapore. Their preliminary data documented a total of 47 window strike between September 2014 and April 2015, with 20 in the central business district (Low, 2015).

Reasons for window strikes

So why do birds crash into windows? Can’t they see the glass? Well surprisingly (or not), windows are invisible to them (Klem, 1989). Birds usually cannot differentiate between reflections and real vegetation. They collide into window panes when flying through vegetation in urban areas, either by trying to reach the reflected greenery or attempting to fly through the corridors to vegetation on the other side (Klem, 2006). In some cases, a territorial bird sees its own reflection as a rival and launches repeated attacks on the window pane (Klem, 2006). Lastly, some migratory birds use celestial patterns to find their way at night. Artificial lights from buildings confuse them, thus attracting these birds to their doom (Low, 2015). On an unrelated note, Singapore actually tops the list as one of the world’s worst light polluted country (Falchi et al., 2016).

Perhaps our lights are a bit too bright?
Photo by Rodney Topor
(Image from:

Contrary to popular belief, most victims of window strikes die not from a broken neck, but instead, due to intracranial haemorrhage. A head on collision ruptures the blood-brain barrier, leading to sub-dural bleeding and brain damage (Klem, 1990a). The most observable external injury is usually a broken beak. And not all birds die from the collision. Some may be stunned or unconscious but then fly off once they recover. Others may merely be startled and fly off immediately (Klem, 1990a).

Ways to prevent window strikes

Over the past few years, many have poured in efforts in search for ways to prevent possible bird-building collision. Here are some of the commonly used methods to counter the window strike problem:

  1. Use of Window Patterns

A relatively simple way to counter window strikes would be to put patterns on the glass, so that the birds can see the windows. In the video below, Christine Sheppard, Collisions Program Manager for the American Bird Conservancy, has being working with her research team to find the most effective window patterns to prevent window collisions.

(Source: YouTube)

Their experimental results show that most birds avoid flying through a horizontal spacing of less than 2 inches (~5cm) or vertical spacing of less than 4 inches (~10cm). Therefore, decal patterns placed uniformly on the window pane or tape strips can be placed to prevent window strikes. UV stickers that are invisible to our eyes but visible to the birds can also be used to maintain the aesthetic of a “clear” glass (Cornell Lab, 2009). In any case, patterns must be on the outside of the window (facing the birds) for it to be effective.

  1. External window accessories

Do you have problems with birds hitting your windows but don’t want to change your window glass or tediously apply decals? Window screens could be your answer! Small-mesh netting or window screening can be placed outside a window, at least 3 inches away from the glass. If the netting is taut enough, birds can bounce off before colliding with the actual glass. External shutters or sun shade can also be used to block the reflection of the glass, making the window entirely opaque when it is not in use (Cornell Lab, 2009).

Bird screen used on window
(Image from:

  1. Switching off unused lights at night

(Source: YouTube)

For tall commercial buildings, like in the Central Business District, you should consider turning off the lights at night. I understand that a lit up building may create a pretty night-time skyline, but this video above may persuade you otherwise. It discusses reasons why birds might prefer to fly at night and how they are attracted to light sources in buildings (Soh, 2014). One campaign to switch off lights in Chicago resulted in an 80% drop in mortality due to bird-building collisions show how effective this strategy can be. Aside from saving birds’ lives, you get to save on electricity too. So it’s a win-win situation for you!

  1. Relocating bird feeders

For bird lovers who have bird feeders at home, you may want to reconsider their placements. If you would like to place the bird feeder nearer to your home, you should keep it within 0.9m from your window (Cornell Lab, 2009). Anything beyond that, the speed they gathered when taking flight from the feeder to the window can result in a fatal impact. For those who are uncomfortable with a bird feeder so near to home, you can alternatively, place your feeder at least 9m away from your windows (Cornell Lab, 2009). This would then ensure that birds will not associate them as possible habitats when they fly off from the feeder. Don’t let your love for birds be the cause of their death!

Final thoughts

Ever run into glass doors because you were not looking? You may have ended up with a bruised nose but to birds, glass can be fatal. Birds are not just simply pretty to look at, they also play important ecological roles. Birds are great seed dispersers and pollinators. So when the bird populations decline, reproduction rates of many plants also decrease too (Tabur & Ayyaz, 2010). Recognising the importance of birds, cities like Toronto, Chicago and New York City have put in place policies and guidelines to mitigate the bird-building collisions problem. Perhaps it’s about time for Building and Construction Authority (BCA) to look into updating its building regulations too?



Cornell Lab. (2009). Why Birds Hit Windows—And How You Can Help Prevent It. Retrieved from

Falchi, F., Cinzano, P., Duriscoe, D., Kyba, C. C., Elvidge, C. D., Baugh, K., & Furgoni, R. (2016). The new world atlas of artificial night sky brightness. Science advances2(6), e1600377.

Klem, D. Jr. (1990). Collisions between birds and windows: mortality and prevention. Journal of Field Ornithology 61:120–128.

Klem, D. Jr. (1990a). Bird Injuries, Cause of Death, and Recuperation from Collisions with Windows. Journal of Field Ornithology 61 (1): 115-19

Klem, D. Jr. (2008). Avian mortality at windows: the second largest human source of bird mortality on Earth. Tundra to tropics: connecting birds, habitats and people.

Klem, D. Jr. (2006). Glass: a deadly conservation issue for birds. Bird Observer34(2), 73-81.

Low, A. (2015). Migratory Bird Collisions in Singapore. Singapore Bird Group. Retrieved from

Loh, J. (2014). Lights Out Effort Reduces Deadly Bird-Building Collisions. VOA News. Retrieved from

Tabur, M. A., & Ayvaz, Y. (2010). Ecological importance of birds.

Marine life in an urban environment

Marine life in an urban environment

by Crystle Wee

When we think about urban environments, we often fail to notice that our marine environments are just as, if not more, influenced by human development. While the focus in urban ecology has been largely dominated by discussions of terrestrial or freshwater environments, it is also vital to think of how urban development shapes marine ecosystems and habitats.

One of the key ways in which marine environments are degraded in Singapore is through widespread land reclamation and the alteration of our natural coastlines by constructed seawalls. After reclamation work is carried out, the area can be more prone to problems such as soil erosion, and this makes it necessary to build more infrastructure to reinforce coastal stability and mitigate erosion. Did you know that around 63% of Singapore’s coastlines are covered by seawalls? We need the seawalls to dissipate the energy in waves so it does not wear away our beaches and coastal areas. But seawalls are very harsh environments that may not support biodiversity the way natural coastal ecosystems do.  Here’s a short infographic I created on land reclamation, which is what I feel is the biggest challenge to marine life in our coastal waters.

Look at changes in reclamation and development of our coastal areas from the 1950s to 2002. Since then, even more reclamation work has been completed, so much so that most of our coastal environments are different from what they were before (Images courtesy of Ria Tan, WildSingapore)


Marine biodiversity that persists despite the pressures of development

Reclamation and development have caused high rates of sedimentation and hence, very turbid waters and Singapore has lost more than 60% of its coral reefs. Nevertheless, Singapore still has an impressive array of marine life: at least 50 sea anemone species, 12 seagrass species and around 255 species of hard corals (Hilton & Manning, 1995; Chou, 2006; Huang et al., 2009). To put that in perspective, we have around a quarter of all hard coral species that can be found in the world!

 Here are pictures of corals I’ve taken in Singapore’s waters! Pretty beautiful right?


Solutions to increase biodiversity in affected areas

The Experimental Marine Ecology Lab in NUS, led by Prof. Peter Todd, is researching methods to increase biodiversity along these sea walls by trying concrete tiles with different complex designs. Depending on the type of surface, the tiles can provide different ecological niches and spaces for a variety of marine organisms to colonise. I like this analogy…imagine a hawker centre in Singapore that only serves chicken rice. Now imagine a similar hawker centre, except this one also serves laksa, satay, roti prata and fishball noodles too! Which one do you think will attract more people? I know I’d definitely prefer the one with more variety! In a similar way, a marine environment with a variety of habitats will attract organisms with different habitat preferences. And so tiles with a greater variety of spaces, are more likely to provide suitable homes for a mixture of different organisms.

These concrete tiles can be a more favourable environment for marine snails and other organisms that typically live in rocky shore habitats. (Images courtesy of the Experimental Marine Ecology Lab, NUS)


If we want to better understand how human processes shape changes in the ecology and function of marine communities, then we need to focus more attention on urban ecology in marine environments. With more studies, hopefully we can think up better ways to develop sustainably and better consider the marine life we share our home with.



Chou L.M. (2006). “Marine habitats in one of the world’s busiest harbours,” in The Environment in Pacific Harbours, E. Wolanski, Ed. Dordrecht: Springer, 2006, ch. 22, pp. 377-391. 

Hilton MJ and S. S. Manning, “Conversion of coastal habitats in Singapore: indications of unsustainable development,” Environmental Conservation, vol. 22, pp. 307-322, 1995.

Huang, D., Tun, K. P., Chou, L. M., & Todd, P. A. (2009). An inventory of zooxanthellate scleractinian corals in Singapore, including 33 new records. Raffles Bulletin of Zoology, 22, 69-80. 

Loke LHL, Todd PA. “Structural complexity and component type increase intertidal biodiversity independently of area.” Ecology. 97 (2016) 383-393.

Loke LHL, Liao L, Bouma TJ, Todd PA. “Succession of seawall algal communities on artificial substrates.” Raffles Bulletin of Zoology. 32 (2016) 1-10.

Loke LHL, Ladle RJ, Bouma TJ, Todd PA. “Creating complex habitats for restoration and reconciliation.” Ecological Engineering. 77 (2015) 307-313.

Loke LHL, Jachowski NR, Bouma TJ, Ladle RJ, Todd PA. “Complexity for artificial substrates (CASU): software for creating and visualising habitat complexity.” PLoS ONE (2014) e87990.

Tan, R. (2008). “Loss of coastal ecosystems” Retrieved April 2017.


Nature Ways

We’ve all heard and talked about Singapore’s nature reserves, nature parks and park connectors. But what about nature ways? I asked three of my BES friends recently and none knew what they are. Alas, these important but rather inconspicuous green corridors have rarely been given a mention: there isn’t even a sign to inform people that they are walking along one! Another reason for their low profile may be their scarcity: there are just 16 in total spanning a relatively short total distance of 68 km (Fig. 1.). Compare that to Singapore’s 78 park connectors totalling 300 km in length (Abdullah, 2015)!

So…what is a nature way?

Just by looking at Fig. 1, the nature ways resemble park connectors but they couldn’t be more different! Many park connectors meander through housing estates and are equipped with user-friendly facilities, such as benches, shelters, cycling tracks and even exercise corners. However, most nature ways are more like enhanced roadside streetscapes (they run alongside roads) and they lack user facilities. Additionally, unlike most park connectors (or nearly anywhere else for that matter) which are planted with trees of the same species and at uniform heights (urban monocultures) to present a “neater” and “orderly” image, nature ways are intentionally planted with a wide variety of plant species and have a more layered vegetation structure to mimic a forest as closely as possible (NParks, n.d.-a) (Fig. 2).

Fig. 1. Map of all the nature ways in Singapore.

Fig. 2. Vegetation structure of a nature way.

Function and importance of nature ways

Why develop nature ways? Well, nature ways are important as they help restore ecological connectivity between fragmented green patches in highly urbanised Singapore. By more closely replicating natural forests, nature ways attract a variety of animals that use them as habitats and wildlife crossings. Animals including birds, reptiles, amphibians, and invertebrates (that occupy different layers) are thus, able to move between green spaces of high biodiversity (NParks, n.d.-a). This facilitates gene flow and dispersal of animals, which are important to reduce inbreeding in otherwise isolated population (Angold et al., 2006).

For example, the longest one, Tengah nature way (TNW), links Bukit Timah Nature Reserve, Central Catchment Nature Reserve and the Western Catchment (NParks, n.d.-b). Surveys conducted to assess its effectiveness found forest-edge species, such as the horsfield’s baron butterfly and common gliding lizard, which were rarely seen before at that location (Chua, 2015), suggesting that the TNW was attracting more animals and facilitating their crossings.

Are there areas for improvement in terms of the design and development of nature ways?

Though nature ways are developed with well-intentions, I feel that there are areas which can be improved. Some of the nature ways (especially long ones like TNW) are not continuous, but occasionally separated by artificial barriers, such as road junctions. This could hinder the movement of animals that are road-phobic and would avoid crossing even the narrowest of roads. Indeed, numerous studies have documented road avoidance behaviour or reluctance to live close to the roads in many animal species, including birds, insects, and mammals (Laurance et al., 2009; Muñoz et al., 2015). Even if the animal does decide to cross the road, it would have to face an onslaught of vehicle traffic and risk being hit by one, which could lead to road mortality. Therefore, it would be better if nature ways could avoid road crossings altogether, but I can only assume that because nature ways should link one green space to another, NParks would have already planned the configuration of nature ways to minimise road crossings.

Additionally, vegetation in some parts of the nature ways is sparse and often sandwiched between the road (some of which have heavy traffic) and pedestrian path (Figs. 3 and 4). This could influence the abiotic conditions in nature ways, resulting in warmer and drier microhabitats as compared to forests because of greater exposure and proximity to impervious surfaces. Noise (vehicles and pedestrians), light (from public street lighting) and air pollution (vehicular emissions and dust) will also reduce the quality of these roadside habitats. Therefore, different environmental conditions compared to natural habitats could deter some species from using the nature ways as crossings or habitats. To reduce these effects, more plants should be planted especially in vegetation-sparse areas to increase vegetation density and improve the quality of re-created habitats along nature ways.

Fig. 3. Portion of the Tengah Nature Way at Bukit Batok Ave 2. Credit: Estella Tan


Fig. 4. Portion of the Chua Chu Kang Nature Way at Teck Whye Ave. Credit: Estella Tan

Finally, I came across a paper by Jain et al. (2014) which argue that the existing method of merely planting bird- and butterfly-attracting species capable of withstanding roadside conditions is inadequate. Instead, planners should also consider the ecological needs of species found in the source and sink fragments before deciding on the types of flora to plant along nature ways (Jain et al., 2014). I concur with the authors, as based on my experience walking along the nature ways, I seldom see a great variety of fauna, and one reason could be the incompatibility of plant species to the fauna found in the connected habitat patches, which deters them from using the nature ways.

Final thoughts

Overall, I am all for the development of nature ways as a habitat de-fragmentation strategy to connect various urban green spaces and conserve Singapore’s biodiversity. The good news is that NParks aims to increase the total length of nature ways to 180 km by 2030 (NParks, n.d.-a)! I do hope that they consider the areas for improvement (as mentioned above) during the development of new nature ways in the future. Also, wouldn’t it be great if park connectors (and other green strips) also adopted the layered vegetation structure and are lined with a wider variety of plant species? That could attract even more wildlife and, in so doing, foster closer connections between people and nature in an urban environment. Finally, I could find very few publicly-available research papers or data on the effectiveness of nature ways, with suggestions for improvement. Perhaps NParks conducts its own internal evaluations, but I do see a lot more room for study (ps. potential FYP topic for anyone who’s interested!).


Abdullah, Z. (2015, September 21). Singapore park connectors reach 300km at 25-year mark. The Straits Times. Retrieved from

Angold, P. G. et al (2006). Biodiversity in urban habitat patches. Science of the Total environment, 360(1), 196-204.

Chua, G. (2015, January 23). How Singapore makes biodiversity an important part of urban life. Citiscope. Retrieved from

Jain, A. et al (2014). Moving away from paper corridors in Southeast Asia. Conservation Biology, 28(4), 889-891.

Laurance, W. F. et al (2009). Impacts of roads and linear clearings on tropical forests. Trends in Ecology & Evolution, 24(12), 659-669.

Muñoz, P. T. et al (2015). Effects of roads on insects: a review. Biodiversity and conservation, 24(3), 659-682.

National Parks Board (NParks). (n.d.-a). Nature Ways. Retrieved from

National Parks Board (NParks). (n.d.-b). Singapore’s longest green corridor will enhance biodiversity in the South West District. Retrieved from

The Singapore Index (SI)

Over the last 30 years, the world’s urban population has been rapidly increasing and is forecasted to reach nearly 5 billion by 2030 (Seto et al., 2012). This has been accompanied by rapid urban land expansion, which is occurring on average twice as fast as urban population growth (Seto et al., 2012). Therefore, if current urban population growth rates remain unchanged, urban land cover is expected to triple in size by 2030 (Seto et al., 2012). This increase would exacerbate biodiversity loss due to even more habitat fragmentation and altered local climates, among other things. However, cities still support some species and can make efforts to conserve them. How then, should cities protect urban biodiversity and ensure their efforts are making progress? Thinking along those lines, I recalled reading a publication by the Centre for Liveable Cities (CLC) (where I used to intern) that discussed biodiversity conservation efforts in cities. Two words caught my attention: “Singapore Index”.

What is the Singapore Index (SI)?

No, this is not about Singapore’s financial stock market. Instead, it involves taking stock of biodiversity in cities. As the name suggests, the SI (also known as City Biodiversity Index) was conceived in Singapore! First proposed at the Conference of Parties (COP) to the Convention of Biological Diversity (CBD) in 2008, the SI is a self-assessment tool with a scoring system for cities to measure and evaluate their progress in biodiversity conservation by comparing with a baseline year (Chan et al., 2014). In 2010, the SI was formally endorsed by the COP (Kohsaka et al., 2013). With the SI, cities can benchmark their progress in reducing the rate of biodiversity loss in urban environments, measure their ecological footprints and identify gaps in biodiversity information (Rodricks, 2010).

In short, it consists of two components (Chan et al., 2014):

  • “Profile of the City” which includes background information of the city
  • 23 indicators in three categories: (1) native biodiversity in the city; (2) ecosystem services provided by biodiversity in the city; and (3) governance and management of biodiversity in the city.

To know more about the SI and indicators used, you can read the user’s manual here! However, if reading a lengthy document doesn’t appeal to you (I totally understand), check out these two videos (will embed), where Dr Lena Chan, Director of the National Biodiversity Centre (NBC) under the National Parks Board, explains how the SI works and why it is useful:

Implementation of the SI

Unsurprisingly, Singapore was one of the first to implement the SI. How did Singapore fare? Not too bad! She scored well in governance, but could improve in terms of ecosystem services and freshwater supplies (Tok, 2011). Other cities have also implemented the SI, including 14 in Japan, India’s Mira Bhainder and Canada’s Edmonton (Kohsaka et al., 2013). However, there were some challenges when it came to implementation. After all, no two cities are exactly alike. Challenges include no clear definition of what defines a “natural area” and “fragmentation”, lack of data on native and invasive species, and difficulties in (1) calculating ecosystem services and (2) determining how much budget to allocate to general environmental causes and biodiversity-specific activities (Kohsaka et al., 2013).

For example, Yokohama is Japan’s second-largest city, making regular comprehensive surveys of biodiversity and terrestrial ecosystems difficult to conduct and seen as unrealistic due to budget constraints (Kohsaka et al., 2013). Indeed, lack of biodiversity data and financial constraints are major challenges in applying the SI especially for cities in developing countries. Even Edmonton, Alberta, Canada, received a relatively low biodiversity and ecosystem services score (Kohsaka et al., 2013). However, one must consider the climate (Edmonton is cold!). This is a reminder that caution should be exercised when comparing scores across cities.

Final thoughts

Overall, despite inevitable compatibility issues with the SI, I feel that it is still a useful tool. Cities may choose to add indicators to the SI or even be inspired to create their own indices to best suit their contexts. Ultimately, the main takeaway is that there is no “one size fits all” index, because it is nearly impossible to include indicators that all cities will have data on. Make it too broad, and the SI will lack depth. Make it too specific or rigid, and it will lack flexibility and applicability. At least the SI recognises the importance of biodiversity in urban environments and spurs cities to keep track of their conservation efforts, a crucial element in the pursuit of sustainable urban development.


Chan, L. et al (2014). User’s Manual on the Singapore Index on Cities’ Biodiversity (also known as the City Biodiversity Index). Singapore: National Parks Board, Singapore.

Kohsaka, R. et al (2013). Indicators for management of urban biodiversity and ecosystem services: city biodiversity index. In Urbanization, biodiversity and ecosystem services: challenges and opportunities (pp. 699-718). Springer Netherlands.

Rodricks, S. (2010). Singapore City Biodiversity Index. Retrieved from

Seto, K. C. et al (2012). Global forecasts of urban expansion to 2030 and direct impacts on biodiversity and carbon pools. Proceedings of the National Academy of Sciences, 109(40), 16083-16088.

Tok, C. (2011). City Biodiversity Index. Retrieved from

Behind those walls

During my exchange in Hong Kong 6 months back, I came across a peculiar sight when I visited the Hong Kong Island region. There were trees on the walls! Tall, massive ones attached to the retaining stone walls! Though I was curious back then, I did not ponder it for too long, as I was distracted by the other delights that Hong Kong could offer. However, when these trees were brought up during the Urban Ecology lecture on urban vegetation, my curiosity was aroused once more.  So, join me as I uncover more about this fascinating phenomenon!

First and foremost, what is a stonewall tree?

“A stonewall tree is a tree that grows on a stone retaining wall with most of its roots spreading on or penetrating through the wall face, and with the trunk base situated within the confines of a wall1.”

Here is an example of a row of stonewall trees in Hong Kong!
(Image from:

The origins of the stone walls

Hong Kong’s unique topography and the lack of developable land meant that urban expansion could only be made possible by land reclamation and terracing the steep hillslopes2. Vertical cutting of the slopes was mostly carried out to obtain usable flat surfaces for urban development, and masonry retaining walls were erected to prevent slope failure2. Hong Kong has about 1 700 masonry retaining walls, mostly in the western and central parts2.The distribution of masonry retaining walls (in red) in western and central parts of Hong Kong
(Image from:


How do trees adapt?

The trees that live on these walls belong to the genus Ficus,i.e., fig trees2. The most common one is the Chinese Banyan (F. microcarpa)2.

The figs that dominate the walls have adaptations to strangling behaviour. In their natural tropical rainforest habitat, their life cycle begins when frugivorous bats and birds deposit droppings containing seeds onto upper branches of other trees, and some germinate3. The seedling starts off as an epiphyte that needs the host tree for a substrate2. Over time, if it has enough resources, the strangler fig will divert its energy to propagating and elongating its aerial roots toward the forest floor2. Eventually, it develops an extensive root system in the soil2. Now that they’ve got a reliable and enhanced root system, the trees can grow quickly and become massive2. Eventually, the aerial roots around the trunk of the host tree thicken and lignify, exerting a strong force, while the host tree exerts an opposite one.  The two opposing forces create so much pressure that they literally strangle the host (that’s how they get their name!), depriving it of water and nutrients, to the point that it dies. A quintessential parasite.


Illustration of how a stranger fig takes over its host plant
(Image from:

A strangler fig in its natural tropical rainforest habitat in Hong Kong!

Back to the stone walls. Basically, the strangler figs substitute the wall for a host tree2. Seeds are deposited in or on the wall2. Of the small fraction that manages to germinate under harsh urban conditions and develop into epiphytes, the natural strangler habit helps their roots penetrate the gaps and joints to reach the soil in the wall core or behind the wall2. This soil allows roots to proliferate, increasing nutrient intake and anchoring the tree2. The lignified aerial roots also interact with the tree’s own branches and trunk to form sturdy and tightly bound networks of root stands and props to support the massive structure2. All in all, strangler figs are pre-adapted to flourish on stone walls.

So why are these trees important?

Hong Kong’s wall trees are considered precious and unique natural assets, exemplifying the harmonious co-existence of culture and nature in an urban environment5. They are also historically important. Some were established in the early 19th century on some of the oldest stone walls4. With traditional masonry wall construction no longer in practice, current threats to demolish and modify these walls further increase the unique historical value of these trees5.  Furthermore, local communities have an attachment to these trees, which they grew up with5, and benefit from the ecosystem services they provide2. Clearly, these trees enhance the urban landscape quality and enrich biodiversity in Hong Kong2.

Check out the designs of these masonry walls!
(Image from:×768.jpg)

A case study of failure

Some of these trees fail, often when they are uprooted during severe weather events2.

For example, in July, 2015, a banyan tree on Bonham street was uprooted and crashed down onto the street, damaging surrounding infrastructure and injuring 2 people7. The video below shows the process of it happening.

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Posted by 現場 - 蘋果突發 on Tuesday, July 21, 2015

(Source: Facebook)

The scene after the tree failure along Bonham street
(Image from:

The Controversy

This incident prompted the Highway Department (HyD) to inspect and manage the conditions of other five trees on this street8. Initially, HyD decided to remove one tree in poor condition and prune the other four8. But just two weeks later, HyD officials decided to remove all the remaining banyan trees, and by the next morning, all four century-old trees were gone9. The official statement released by the HyD stated that they found signs of the walls weakening, which posed a risk of imminent tree collapse and a threat to public safety8. This decision ignored recommendations from experts6, including from Civil Engineering and Development Department, which found no evidence of instability 10.


The remaining stumps of the 4 Chinese Banyans
(Image from:

The not-so-happily-ever-after ending?

(Source: Youtube)

In the aftermath of this event, the local community mourned the loss of the banyans, expressing their feelings by posting notes and attaching balloons to the roots or stumps or whatever was left of the trees.

Key takeaways and Call to Action
  1. The decision and handling of this incident by the Government lack transparency. Proper explanations should be given. If there were any potential risk to public safety due to the walls or the trees, then the Government should have conducted and publicised a tree and wall evaluation report to justify their actions.
  2. The Government should engage the public and experts for consultation. Even though a panel of experts was consulted, the relevant authorities ignored findings that the remaining four trees pose no danger6. The public was not consulted despite its affinity for the trees.
  3. The Government should formulate a comprehensive conservation guideline or plan to protect and conserve the wall trees in Hong Kong, and give experts a greater say.
  4. Public education is key in raising awareness and appreciation of the natural and historical significance of the trees. The public should be thoroughly briefed on who to contact when they spot an issue with the trees.
  5. Increased monitoring should be used to ensure that walls are sturdy enough to support the trees, and trees should be maintained so that their weight is not excessive.
Final thoughts

While scouring for more information on stonewall trees, I stumbled on and became embroiled in the controversy of Hong Kong government’s actions involving the stonewall trees. It became clear to me that there is a government-public disconnect, in that the authorities did not consult the local community. But the government argued that it was acting in the interests of public safety, and not in the interests of public preferences6. A question to ask is: are we wrong to criticise the government’s mentality that prevention is better than cure, even at the expense of conservation? If so, then what is the best course of action?

For more information about stonewall trees, do check out this infographic!


1Jim, C.Y. (1998). Old stone walls as an ecological habitat for urban trees in Hong Kong. Landscape and Urban Planning 42(1): 29-43.

2Jim, C.Y (2012). Study on Stonewall Trees: Maintenance Approach for the Six Stonewall Trees on Slope no. 11SW-A/R577, Bonham Road. Highways Department Government of the HKSAR. Retrieved from

3Jim, C. Y. (2014). Ecology and conservation of strangler figs in urban wall habitats. Urban Ecosystems, 17(2), 405-426.

4Lo, A. Y., & Jim, C. Y. (2015). Community attachment and resident attitude toward old masonry walls and associated trees in urban Hong Kong. Cities, 42, 130-141.

5Greening, Landscape and Tree Management Section Development Bureau. (2013). Management Guidelines for Stonewall Trees.  Retrieved from

6Time Out Hong Kong. (2016). Should Hong Kong’s century-old stonewall trees be removed?. Retrieved from

7Kilpatrick, R. (2015). Video: The moment Hong Kong’s biggest ‘wall tree’ came crashing down. Hong Kong Free Press. Retrieved from

8Wong, V. (2015). Bonham Road Banyan trees removed after cracks in stone wall appear. Hong Kong Free Press. Retrieved from

9Chan, B. (2015). It’s a saw point: why Hong Kong’s urban trees need managing better. South China Morning Post. Retrieved from

10Bauhinia Foundation Research Centre. (2015). Cutting down of stonewall trees causes controversy on tree management policy. Retrieved from

A day of fun and discovery at Waterways Watch Society’s Family Carnival

Last Saturday morning, a group of excited friends travelled to Kallang Riverside Park to participate in Waterways Watch Society’s (WWS) first ever family carnival. We were invited by Li Jean who used to intern at the organisation. The river clean-up kayaking event had caught our attention and we signed up for it because we thought, “why not do something good for the environment while having fun?”

Reservoirs comprise a significant component of Singapore’s urban freshwater habitats. In fact, they have been found to have greater diversity of freshwater mollusc species as compared to forest streams, ponds and monsoon canals (Clements et al., 2006).

During the briefing session before we set off, participants were educated on the impacts of litter on aquatic organisms. We were told that litter, such as aluminium cans, form a surface for the eggs of the golden apple snail, Pomacea canaliculata, to be stuck in. The eggs hatch inside the cans, and when the snails get bigger they are unable to escape and eventually die inside. We were all urged to pick up any cans we find, give them a rattle to see if there are any trapped golden apple snails, and then cut up the cans to free the snails. This then sparked a discussion on whether we should actively save invasive species.

The golden apple snail was introduced into Singapore most likely because of the pet trade (Yeo & Chia, 2010) and has now exploded in numbers in many reservoirs, ponds and drains across Singapore (Tan et al., 2013). It is listed as one of the world’s 100 most invasive species (Lowe et al., 2000). If you have ever seen clumps of tiny pink round balls sticking to the sides of river banks, those are the eggs of the golden apple snail! Since the introduction of the golden apple snail, the abundance of the native snail, Pila scutata declined rapidly, which might be due to the presence of the invasive apple snail (Chan, 1996; Tan et al., 2012).

So back to the question. Are invasive species in general worthy of saving? Perhaps the creation of non-native habitats such as reservoirs made these alien animals ‘native’ to that kind of habitat? If so, then they might be considered native in that context. Or maybe it is more of a morality issue, i.e., we should help any animal in peril regardless of the damage it does to the ecosystem.

As we went on our kayaking adventure, we did not find any apple snail-containing cans, but we were shocked by how much rubbish we saw floating on the water surface and half-submerged. I had always thought that Singapore’s waterways are clean, especially the reservoirs where we also obtain our drinking water from. But this journey brought us closer to the litter that is hidden from the sight of most park users. We learnt that trash gets into our waterways via different paths, such as being blown in from land or carried in pipes that discharge water into the river.

As I was gliding across the river with my partner and trying to spot litter, I realised that riparian vegetation actually traps quite a lot of trash, making it difficult to remove. Thus, by accumulating trash, riparian vegetation could have made our waterways dirtier. Even so, we cannot deny the benefits that these plants bring, as they help to reduce erosion and provide breeding grounds and shelter for otters and birds (NParks, 2009). Another realisation I made was that most of the time, we only pick up visible litter, but upon closer inspection, I saw a lot of submerged trash – it would normally get missed. This litter, including plastic bags and straws, can pose a huge threat to wildlife. For example, WWS volunteers told us about the many times when they had to free fish stuck in plastic bags. I learnt that even though paid contractors and WWS volunteers regularly clean up the Kallang River, the volume of rubbish never seems to dwindle.

At the end of our 40-minute session of kayak clean-up, the total weight of rubbish we all collected totalled 16 kg. That might not seem like much, but we were told that contractors collect about 10 tonnes of trash from the Kallang River every day! It is undeniable that waterways in and near cities will tend to have greater pollution as compared to those in the forest. But modified habitats, such as our canals and reservoirs, are increasingly becoming important sites for native biota, such as the famous smooth coated otters, Lutrogale perspicillata, whose return signifies cleaner waterways in Singapore (BBC News, 2016). Therefore, I believe that one method to ensure the integrity of our urban freshwater ecosystem and possibly boost species richness is to maintain litter-free habitats.

So, for this World Water Day, apart from reinforcing our water-saving habits, let us remember not to litter and to pick up any trash we find near waterbodies, so they do not get washed or blown into our rivers and reservoirs!


You might recognise some of us in the photo to be from LSM4265!

Photo credit: Gwendolyn Chow


Literature cited

BBC News (2016) Singapore’s celebrity urban otter family. (Accessed 21st March 2017).

Chan SY (1996) Some freshwater gastropods of Singapore. Of Sea and Shore, 18: 184–187.

Clements R, Koh LP, Lee M, Meier R & Li D (2006) Importance of reservoirs for the conservation of freshwater molluscs in a tropical urban landscape. Biological Conservation, 128(1): 136-146.

Crome F, Isaacs J & Moore L (1994) The utility to birds and mammals of remnant riparian vegetation and associated windbreaks in the tropical Queensland uplands. Pacific Conservation Biology, 1(4): 328-343.

Lowe S, Browne M, Boudjelas S & De Poorter M (2000) 100 of the World’s Worst Invasive Alien Species, a Selection from the Global Invasive Species Database. Invasive Species Specialist Group (ISSG), a specialist group of the Species Survival Commission (SSC) of the World Conservation Union (IUCN), Auckland, New Zealand, pp. 1–12.

National Parks Board (NParks) (2009) Singapore’s National Biodiversity Strategy and Action Plan. (Accessed 21st March 2017)

Tan SK, Chan SY & Clements GR (2012) A Guide to Snails and Other Non-marine Molluscs of Singapore. Singapore Science Centre, Singapore, 176 pp.

Tan SK., Lee YL & Ng TH (2013) The status of the apple snail, Pila scutata (Gastropoda: Ampullariidae) in Singapore. Nature in Singapore, 6: 135-141.

Yeo DCJ & Chia CSW (2010) Introduced species in Singapore: An overview. COSMOS, 6: 23–37.



You’re in my way!

Figure 1. The forest in my backyard

Singapore, the Garden City of Asia, boasts its lush greenery and abundant biodiversity. But all is not always as such. The recent toppling of a tembusu tree at the Singapore Botanic Gardens sparked major concern in Singapore when it killed a person and injured four others. This is not the first incident of tree fall that has cost a life or property damage. In fact, these incidents began as early as 2013.

Four years ago, a forest tree fell right into my house. That’s right, urban ecology in my backyard. I remember walking into the kitchen to get my fix of caffeine when a slow, loud and unusual creaking sound resonated from the backyard. I headed out to investigate. A huge tree and its massive foliage came tumbling down with a loud whoosh. Roofs were broken, fences were bent and branches were everywhere. Fortunately, no one was injured. (Personally, it was an amazing experience to see a tree fall (without getting injured), but it was a nightmare for my parents.)

This year, the trees came back and vegetation crept closer to my house. The fall of the tembusu sent my neighbourhood into another email frenzy with the National Parks Board (NParks). They wanted their backyards to be safe spaces. This meant the trimming of trees and the removal of vegetation from the forest. Their unhappiness and persistence of the matter left me in a dilemma between the interest of my neighbourhood and that of the biota in our backyards. My silent dilemma came to an end when a decision was made. Just last week, workers came with their equipment and started sawing down trees in the forest which were within 5 metres of the neighbourhood. The result? A barren forest edge, the loss of heritage trees, a noticeable decrease in bird calls, macaques walking along the fence, and what the neighbourhood wanted: safer backyards. It is interesting to note that macaques have never been seen along the fence, apart from this week. Did the removal of trees disturb their habitat and cause them to move?

Figure 2. The forest after the removal of trees and vegetation


Figure 3. Macaque spotted on the fence

This issue taught me that the complaints never stop. People perpetually seem to have problems with living with nature. Rarely do they take into account the geographical context of their location. Singapore is located in the vibrant tropics, with a beautiful diversity of plants and animals. We have the North-East monsoon which sends thunderstorms and turbulent winds to our island twice a year. It sways the trees in an exotic dance against the backdrop of falling leaves. This is nature. Perhaps, we should learn to treasure the invaluable biota of our land and not take them for granted. Perhaps, we should first learn about nature and how to approach it before we let our fears decide what is best. Perhaps, we should ask ourselves, are they in our way, or are we in their way?

Given the high density and limited space in Singapore, the physical line and distance between humans and wildlife will only be closer and closer. We can choose how to react to it – in anger or appreciation. What will your choice be today?



MIN, C. (2017). Tree falls on parked cars at Amoy Street. The Straits Times. Retrieved 17 March 2017, from

Woman killed by tree fall moved to Singapore in 2013. (2017). The New Paper. Retrieved 17 March 2017, from

YANG, C. (2017). Woman killed by tembusu tree at Singapore Botanic Gardens last worked at Mastercard. The Straits Times. Retrieved 17 March 2017, from


Coexist or not – My personal experience with Singapore’s feathery “pests”

With approximately 40% of urban ecology literature focused on birds, it is of no doubt birds hold a prominent place in urban ecology. As an urban city, Singapore houses many urban birds. As a child, the local urban bird that had the largest impression on me was the house crow (Corvus splendens). In my childlike eyes, they were large and frightening. In an attempt to curb the exploding population of the invasive house crow, the Singapore government has used culling since 1973 (Brook et al., 2003). I actually witnessed one such culling event in my estate. I remember the loud gunshot sounds and being told by my mother that they were shooting the crows.

As a young adult now, I realise that I do not notice the house crow as often as before. Instead, everywhere I look on the streets is the ubiquitous myna. However, it may not be widely known among locals that Singapore actually has two species of myna, the common myna (Acridotheres tristis) and the Javan myna (A. javanicus). As a Bachelor of Environmental Studies student, I am embarrassed to say that I only learned this fact a few months ago. Earlier, I had the misconception that Singapore had only one species of myna, which was introduced. Yet, this is not true. The Javan myna was introduced to Singapore around 1924, while the common myna is native to Singapore (Yap, 2003).

In fact, the myna we often observe all around us is the Javan myna. In the 31st Annual Bird Census conducted last year by the Bird Group of the Nature Society (Singapore), the Javan myna was found to be the most abundant. 900 Javan mynas were observed that day, making up 13.4% of all birds detected in the census (Bird Group of the NSS, 2016). On the other hand, house crow was in 11th place with 138 counts, making up approximately 2.05% (Bird Group of the NSS, 2016). Thus, it is evident that the local bird diversity is currently dominated by the Javan myna. The common myna did not even place among the top 20 abundant birds counted in the census.

Javan myna (A. javanicus) [Photograph by: Kavi Nanda]

I have always considered both the house crow and the Javan myna as pests. Not only are they not aesthetically pleasing, they are always congregating around hawker centres and pecking away at food scraps left behind on the tables. In other countries, the Javan myna is an agricultural pest, feeding on cultivated fruits and young crops. In Singapore, the main problems it causes are noise, droppings associated with communal roosts and competition with native species.

Upon learning in ENV2102 Environmental Law, Policy, Governance & Management that Singapore’s legislation (Statute 5 of the Wild Animals and Birds Act ) legalises the killing of species specified in the Schedule, I actually supported the idea of culling Javan mynas. Other than the Javan myna, five other species have been specified in the Schedule, namely the house crow, the feral pigeon (Columba livia), the purple-backed starling (Sturnus sturninus), the Philippine glossy starling (Aplonis panayensis) and the common myna.

My dislike for the species grew when I begin to observe a Javan myna on the ledge right outside my window. It kept coming back day after day, making loud calls frequently. Its calls annoyed me when I was studying and I would try to chase it away. One day, I saw it entering the electrical box (which is not completely covered) at the lift lobby with a twig. I figured the myna must be nesting in there, and that is why it keeps appearing at my window, which is right next to the lift lobby.

Just last week, I noticed this handwritten sign by a neighbour on the electrical box. Upon closer inspection, I heard chicks chirping! As I was taking the photograph below, the myna was calling from the nearby ledge, seemingly agitated by my presence and protective of its chicks. Having always thought that most Singaporeans would share my dislike for the myna, I was surprised that one of my neighbours was compassionate for it. It made me reconsider my dislike for the species.

Handwritten note by a neighbour pasted on the electrical box in the lift lobby

Human-wildlife conflict in urban areas is a prevalent issue in Singapore, with the recent uproar over the culling of local jungle fowls (refer to Lijean’s post to find out more). Being an invasive species, the Javan myna is here to stay. Taking the example of my neighbour, I may not be able to love the species but I think I can slowly learn to coexist with my feathery neighbours. Looking forward to the opportunity to see the adult myna and chicks in action!

Bird Group of the Nature Society (Singapore) (Bird Group of the NSS). (2016). Report on the 31st Annual Bird Census. Retrieved from:
Brook, B. W., Sodhi, N. S., Soh, M. C. K. & Lim, H. C. (2003). Abundance and Projected Control of Invasive House Crows in Singapore. The Journal of Wildlife Management, 67(4): 808-817.
Yap, C. A. M. (2003). A Study of the Changes in the Range Size of White-vented Mynas in Singapore. The Raffles Bulletin of Zoology, 51(1): 159-163.

Crested goshawks: Urban Delight

On January 2017, in the heartlands of Bedok, a pair of crested goshawks decided to make a new home for their family. In this blog post, I would like to share a few photos taken by our local nature photographers and also discuss how this bird has managed to thrive in the urban environment.

The crested goshawk, Accipiter trivirgatus, is a resident raptor in Singapore with a range that extend from South to Southeast Asia. Growing up to 43 cm, some diagnostic features include a long crest and a buff vent. The Crested Goshawk usually resides and breeds in lowland forests and woodlands.

In this urban ecology special, our feathered friends managed to nest successfully in the urban environment in a tall tree adjacent to a HDB right in Bedok North.

Photograph by: GaoJian LiuJia (facebook)

In order to nest successfully, a few conditions have to be met. One of them is an appropriate nest site. Thanks to our nation-wide urban greenery plan, we see many tall trees in our city, thereby providing refuge and shelter to build a nest. This, along with the many shrubs in the vicinity, ensures that nesting materials can be obtained conveniently and easily.

Another condition is a convenient food source for both parents and the chicks. Our urban biodiversity is very much made up of ‘pest’ species like crows, Javan mynas and pigeons. Would these pest birds be an ideal diet for our goshawks?

Photograph by: Adrian Tan (facebook)

From the photographs taken by our nature photographers above and many more on the Internet, it can be seen that the main diet of these goshawks are Javan mynas and fruit bats. These animals are very common in our urban landscape, possibly increasing hunting success.

Photograph by: Tony Chua (facebook)

With such an abundance of food , little threat of predation on both eggs and chicks (the domestic cats couldn’t climb up such a high tree) and nest defence by the parents, the two chicks successfully fledged and were taught to preen and hunt by their parents.

As the juveniles were learning to fly for the first time, there were many occasions when they fell to the ground. This caused quite an excitement among the goshawks’ human neighbours as they were able to witness this important moment of a fledging’s life. Many members of the general public would have never seen a crested goshawk before, and to see their life-cycle first hand was indeed a delight! From the photograph below we see the goshawk’s neighbours of all ages curiously fascinated by its presence and yet keeping a distance from it (possibly instructed by our nature photographers). However, with the crowd swarming a single bird, would the young goshawk be heavily stressed out?

Photograph by: Jeremiah Loei (facebook)

Hopefully, this successful nesting in the heartlands reminded many Singaporeans that we do have wildlife thriving in our tiny island. In the case of the goshawks, it shows that wildlife can indeed coexist with people in the urban environment, and breed successfully due to the year-round abundance of prey and low predation risk. I also hope that this nesting event raises awareness about conserving the wildlife we have in Singapore and help us appreciate the existence of natural landscapes even in our heavily urbanised environment.


A recent study by Lin et al. (2015) also found increased breeding success by crested goshawks in the urban environment in Taiwan. Similar to our local goshawks, factors that improve breeding performance include lower predation, high food supply and shelter from inclement weather. They even found that the urban environment advances the goshawks’ breeding schedule, coincidently avoiding the rainy season. The crested goshawk could be adapting fantastically to the new urban environment globally.

You can read the paper here:

Unfortunate “Noisy” Animals

In last week’s lecture, we learnt about urban biodiversity and how the abiotic urban environments affect some species. The alteration of bird and frog calls in frequency, timing and amplitude makes them susceptible to other threats which include higher risk of predation. This reminded me of the latest “human-wildlife conflict” in Singapore: Free-roaming chickens vs. Sin Ming Residents.
The free-roaming chickens were being culled after the Agri-Food & Veterinary Authority of Singapore (AVA) received 20 complaints from the residents (Toh, 2017)- and other reasons such as threat to public health, and the endangered native Red Junglefowl (Tan, 2017). Many debated that the culling of chickens was not clearly justified and actions were taken without much investigation (Toh, 2017). Several people also suggested that the chickens were in fact the Red Junglefowl and that the authorities were simply covering up (Koh, 2017). NParks and AVA refuted back by stating that the Red Junglefowls are KNOWN to occur only in Pulau Ubin and the Western Catchment area and that the differences between a common chicken and the Junglefowl (Tan, 2017).
However….. there was a footage that was used as evidence to prove that the chickens were the Red Junglefowl: 

Unfortunately, nothing can be done now to save the chickens. The complaints were likely to be the sentiments of a minority of the residents but we can indeed see how efficient the government agencies were at addressing the complaints. I was reminded of this news as I was considering the likelihood of residents’ complaining the bird and frog species which alter their calls in order to adapt to urban environment. Should the consequences of alteration of calls include human removal then? (This might sound silly to you but I am just considering the possibility of it happening). However, the fact that we humans decide the survival of the animals with just a complaint shows how powerful we are as a driver in shaping the urban wildlife community. Additionally, the authorities should not simply assumed that the Red Junglefowl occur only in several areas. Sin Ming is very near to the Catchment. There is indeed a possibility that the chickens were the Red Junglefowl! More investigation is needed when addressing such complaints about the animals and the welfare of the animals should be of equal priority. If the chickens were indeed the endangered species, can we trust the authorities in fostering and safeguard urban biodiversity? 
In my opinion, the culling of the free-roaming chickens simply promotes the residents’ intolerance to animals’ presence in the urban area. This will perhaps have implications on the fostering urban wildlife. The free-roaming chickens had lived in the area for decades but were still culled. What can we expect as encroachment to nature areas increase which increases the chances of people encountering more unusual wildlife??
The presence of the free-roaming chickens could or should be used as a material to educate the public of the way to co-exist with urban animals. The public should be guided to accept the presence of urban wildlife. This is especially so when Singapore is an urban jungle and many of us do not frequently connect and interact with nature. Although many were against of the culling, many suggested relocating the chickens instead. This shows that people who are in favour of protecting the wildlife may not necessary be open to sharing spaces with them. This is a huge obstacle in urban biodiversity conservation.
Khew, C. (2017, February 3). Chicken culling issue raises need for more awareness. Asiaone. Retrieved from:
Koh, W.T. (2017, February 3). Common chickens or red junglefowl. The Middle Ground. Retrieved from:
Tan, A. (2017, February 2). Free-ranging chickens may be culled. The Straits Times
Retrieved from:
Toh, E.M. (2017, February 1). ‘Noisy chickens’ in Sin Ming Avenue put down after residents’ complaints. Retrieved from: